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Application Analysis of Thin Film Capacitor in New Energy Vehicle

New energy vehicles refer to the use of unconventional vehicle fuel as a power source. New energy vehicles include hybrid electric vehicles, pure electric vehicles, fuel cell electric vehicles, hydrogen engine vehicles, other new energy sources (such as high-efficiency energy storage, dimethyl ether) vehicles and other products.
Motor, battery and motor control technology are the three core technologies of new energy vehicles. The core of motor control technology is the need for high-efficiency motor-controlled inverter technology. The high-efficiency motor-controlled inverter technology needs a powerful IGBT module and a matching DC support capacitor.

Technical Advantages of Thin Film Capacitors

The electrolytic capacitors were used in the early DC supporting film capacitors. With the development of the film capacitors technology, especially the development of the base film technology and the emergence of the partitioning technology, not only the volume of the film capacitors became smaller and smaller, but also the voltage withstanding level of the products remained at a considerable level. Nowadays, more and more companies adopt high temperature polypropylene film capacitors. As DC support capacitors, a typical example is the improvement of RIUS model of Toyota, while the typical representative of domestic automotive enterprises are BYD F3DM and E6, which use thin film capacitors as DC support capacitors. The filter capacitors used by the first generation of Toyota Prius are electrolytic capacitors. From the second generation, thin film filter capacitor banks have been used.
A. The product has good safety and strong overpressure resistance.
Due to the self-healing phenomenon of thin film capacitors, and the design of thin film capacitors is in accordance with the standard of 1EC61071, the surge resistance capacity of capacitors is greater than the rated voltage of 1.5, and the capacitance adopts the split film technology. See Fig. 4, the short-circuit breakdown phenomenon of capacitors will not occur in theory, which greatly improves the safety of such capacitors. The typical failure mode is open circuit. The anti-peak voltage capability of capacitors in specific applications is also an important indicator of capacitance. In fact, for electrolytic capacitors, the maximum allowable surge voltage is 1.2 times, which forces users to consider peak voltage rather than nominal voltage.
B. Good temperature characteristics, wide range of product temperature, from - 40C - 105C
The high temperature polypropylene film used for DC supported thin film capacitors has temperature stability that polyester film and electrolytic capacitor do not have, as shown in Fig. 5 and Fig. 6.
As can be seen from Fig. 5, the capacitance of polypropylene film capacitors decreases as a whole with the increase of temperature, but the proportion of the decrease is very small, about 300 PPM/C; while the capacity of polyester film varies greatly with temperature, whether at high or low temperatures, ranging from + 200 to + 600 PPM/C.
C frequency characteristic is stable and the product has good high frequency characteristic.
At present, the switching frequency of most controllers is about 10KHZ, which requires the high frequency performance of the products. For electrolytic capacitors and polyester film capacitors, this requirement is a difficult problem.
D. No polarity, able to withstand reverse voltage
The electrodes of thin film capacitors are nano-sized metals plated on thin films, and the products are non-polar. Therefore, it is very convenient for users to consider the problems of positive and negative electrodes. For electrolytic capacitors, if the reverse voltage of more than 1.5 times Un is applied to the electrolytic capacitors, chemical reactions within the capacitors will occur. If the voltage lasts long enough, the capacitor will explode or the electrolyte will flow out as the internal pressure of the capacitor is released.
E. High rated voltage, no need for series and balanced resistance
In order to improve the output power, bus voltage of hybrid electric vehicle and fuel cell vehicle is increasing. Nowadays, the typical voltage of batteries for motors in the market is 280V, 330V and 480V. The capacitors matched by them are different from those of different manufacturers, but they are generally chosen as 450V, 600V, 800V, with capacitance ranging from 0.32mF to 2mF, while the rated voltage of electrolytic capacitors is not higher than 500V. Therefore, when bus voltage is higher than 500V, the system can only improve capacitor banks by series electrolytic capacitors. Pressure level. In this way, not only the volume and cost of the capacitor bank are increased, but also the inductance and ESR in the circuit are increased.
F Low ESR, strong ripple current resistance
Thin film capacitors are larger than 200 mA uF, and electrolytic capacitors have a ripple current capacity of 20 mA uF, which can greatly reduce the capacity of capacitors needed in the system. Domestic manufacturers such as Xiamen Farah's main products are now 04-0.5m2, with the maximum ripple current ranging from tens of amperes to hundreds of amperes.
G. low ESL
The low inductance design of inverters requires that DC-Link capacitors, the main component of the inverters, have extremely low inductance. The high performance DC-Link DC filter film capacitor reduces its self-inductance to the lowest level by integrating buses into the capacitor module ("30nH"), which greatly reduces the oscillation effect at the necessary switching frequency. Therefore, the absorption capacitance parallel to DC-Link capacitor is often omitted, and the capacitor electrodes are directly connected to GBT.
H. Strong ability to resist surge current
It can withstand instantaneous high current. The ability of product surge current temperature and mechanical shock can be improved by adopting wave splitting technology and capacitance coating and thicker edge technology.
J. Long life
The non-ageing property of thin film determines the long life of thin film capacitors. Especially at rated voltage and temperature, the service life of thin film capacitors is more than 15 000 hours. If the average service life is 30 Km/H, the service life of thin film capacitors can be 450 000 Km. The life of capacitors is enough for the driving mileage of automobiles.
Thin Film Sensor

This kind of thin film sensor has many functions in our daily communication. In our actual daily life